Strength and muscle specificity of a compact promoter derived from the slow troponin I gene in the context of episomal (gutless adenovirus) and integrating (lentiviral) vectors

Muscle-Specific Promoters for Gene Therapy

Many genetic diseases that are responsible for muscular disorders have been described to date. Gene replacement therapy is a state-of-the-art strategy used to treat such diseases. In this approach, the functional copy of a gene is delivered to the affected tissues using viral vectors. There is an urgent need for the design of short, regulatory sequences that would drive a high and robust expression of a therapeutic transgene in skeletal muscles, the diaphragm, and the heart, while exhibiting limited activity in non-target tissues. This review focuses on the development and improvement of muscle-specific promoters based on skeletal muscle α-actin, muscle creatine kinase, and desmin genes, as well as other genes expressed in muscles. The current approaches used to engineer synthetic muscle-specific promoters are described. Other elements of the viral vectors that contribute to tissue-specific expression are also discussed. A special feature of this review is the presence of up-to-date information on the clinical and preclinical trials of gene therapy drug candidates that utilize muscle-specific promoters.

A Muscle Hybrid Promoter as a Novel Tool for Gene Therapy

Gene therapy is a promising strategy to cure rare diseases. The lack of regulatory sequences ensuring specific and robust expression in skeletal and cardiac muscle is a substantial limitation of gene therapy efficiency targeting the muscle tissue. Here we describe a novel muscle hybrid (MH) promoter that is highly active in both skeletal and cardiac muscle cells. It has an easily exchangeable modular structure, including an intronic module that highly enhances the expression of the gene driven by it. In cultured myoblasts, myotubes, and cardiomyocytes, the MH promoter gives relatively stable expression as well as higher activity and protein levels than the standard CMV and desmin gene promoters or the previously developed synthetic or CKM-based promoters. Combined with AAV2/9, the MH promoter also provides a high in vivo expression level in skeletal muscle and the heart after both intramuscular and systemic delivery. It is much more efficient than the desmin-encoding gene promoter, and it maintains the same specificity. This novel promoter has potential for gene therapy in muscle cells. It can provide stable transgene expression, ensuring high levels of therapeutic protein, and limited side effects because of its specificity. This constitutes an improvement in the efficiency of genetic disease therapy.

Gene Transfer of ZMapp Antibodies Mediated by Recombinant Adeno-Associated Virus Protects Against Ebola Infections

Vectored delivery of the ZMapp antibody cocktail (c2G4, c4G7, and c13C6) by using recombinant adeno-associated viruses (rAAVs) could be useful for preventive immunization against Ebola virus infections because rAAVs can generate long-term antibody expression. Three rAAVs (serotype 9) encoding chimeric ZMapp antibodies were produced by triple-plasmid transfection up to 10 L-scale in WAVE bioreactors using HEK293 cells grown in suspension/serum-free conditions. Efficacy of AAV-c2G4 via intravenous (i.v.), intramuscular (i.m.), and intranasal (i.n.) routes of administration was evaluated in mice with two different doses of 2.7 × 10¹⁰ and 13.0 × 10¹⁰ vector genomes (vg). The best protective efficacies after Ebola challenge were obtained with the i.v. and i.m. routes. Serum concentrations of ZMapp antibodies positively correlated with survivability. Efficacy of the rAAV-ZMapp cocktail was then evaluated at a higher dose of 30.0 × 10¹⁰ vg. It conferred a more robust protection (90% i.v. and 60% i.m.) than rAAV-c4G7 (30%) and rAAV-c13C6 (70%), both administered separately at the same dose. Delivery of rAAV-c2G4 alone achieved up to 100% protection (100% i.v. and 90% i.m.) at the same dose. In conclusion, the preventive treatment was effective in mice. However, no advantage was observed for using the rAAV-ZMapp cocktail in comparison to the utilization of the single rAAV-c2G4.

Adaptation of vectors and drug-inducible systems for controlled expression of transgenes in the tumor microenvironment

Biological therapies based on recombinant proteins such as antibodies or cytokines are continuously improving the repertoire of treatments against cancer. However, safety and efficacy of this approach is often limited by inappropriate biodistribution and pharmacokinetics of the proteins when they are administered systemically. Local administration of gene therapy vectors encoding these proteins would be a feasible alternative if they could mediate long-term and controlled expression of the transgene after a single intratumoral administration. We describe a new vector platform specially designed for this purpose. Different combinations of transactivators and promoters were evaluated to obtain a fully humanized inducible system responsive to the well-characterized drug mifepristone. The optimal transactivator conformation was based on DNA binding domains from the chimeric protein ZFHD1 fused to the progesterone receptor ligand binding domain and the NFkb p65 activation domain. The expression of this hybrid transactivator under the control of the elongation factor 1α (EF1α) or the chimeric CAG promoters ensured functionality of the system in a variety of cancer types. Expression cassettes with luciferase as a reporter gene were incorporated into High-Capacity adenoviral vectors (HC-Ad) for in vivo evaluation. Systemic administration of the vectors into C57BL/6 mice revealed that the vector based on the EF1α promoter (HCA-EF-ZP) allows tight control of transgene expression and remains stable for at least two months, whereas the CAG promoter suffers a progressive inactivation. Using an orthotopic pancreatic cancer model in syngeneic C57BL/6 mice we show that the local administration of HCA-EF-ZP achieves better tumor/liver ratio of luciferase production than the intravenous route. However, regional spread of the vector led to substantial transgene expression in peritoneal organs. We reduced this leakage through genetic modification of the vector capsid to display RGD and poly-lysine motifs in the fiber knob. Safety and antitumor effect of this gene therapy platform was demonstrated using interleukin-12 as a therapeutic gene. In conclusion, we have developed a new tool that allows local, sustained and controlled production of therapeutic proteins in tumors.

Virus-Like Particles Derived from HIV-1 for Delivery of Nuclear Proteins: Improvement of Production and Activity by Protein Engineering

Virus-like particles (VLPs) derived from retroviruses and lentiviruses can be used to deliver recombinant proteins without the fear of causing insertional mutagenesis to the host cell genome. In this study we evaluate the potential of an inducible lentiviral vector packaging cell line for VLP production. The Gag gene from HIV-1 was fused to a gene encoding a selected protein and it was transfected into the packaging cells. Three proteins served as model: the green fluorescent protein and two transcription factors-the cumate transactivator (cTA) of the inducible CR5 promoter and the human Krüppel-like factor 4 (KLF4). The sizes of the VLPs were 120-150 nm in diameter and they were resistant to freeze/thaw cycles. Protein delivery by the VLPs reached up to 100% efficacy in human cells and was well tolerated. Gag-cTA triggered up to 1100-fold gene activation of the reporter gene in comparison to the negative control. Protein engineering was required to detect Gag-KLF4 activity. Thus, insertion of the VP16 transactivation domain increased the activity of the VLPs by eightfold. An additional 2.4-fold enhancement was obtained by inserting nuclear export signal. In conclusion, our platform produced VLPs capable of efficient protein transfer, and it was shown that protein engineering can be used to improve the activity of the delivered proteins as well as VLP production.

miR-434-3p and DNA hypomethylation co-regulate eIF5A1 to increase AChRs and to improve plasticity in SCT rat skeletal muscle

Acetylcholine receptors (AChRs) serve as connections between motor neurons and skeletal muscle and are essential for recovery from spinal cord transection (SCT). Recently, microRNAs have emerged as important potential biotherapeutics for several diseases; however, whether miRNAs operate in the modulation of AChRs remains unknown. We found increased AChRs numbers and function scores in rats with SCT; these increases were reduced following the injection of a eukaryotic translation initiation factor 5A1 (eIF5A1) shRNA lentivirus into the hindlimb muscle. Then, high-throughput screening for microRNAs targeting eIF5A1 was performed, and miR-434-3p was found to be robustly depleted in SCT rat skeletal muscle. Furthermore, a highly conserved miR-434-3p binding site was identified within the mRNA encoding eIF5A1 through bioinformatics analysis and dual-luciferase assay. Overexpression or knockdown of miR-434-3p in vivo demonstrated it was a negative post-transcriptional regulator of eIF5A1 expression and influenced AChRs expression. The microarray-enriched Gene Ontology (GO) terms regulated by miR-434-3p were muscle development terms. Using a lentivirus, one functional gene (map2k6) was confirmed to have a similar function to that of miR-434-3p in GO terms. Finally, HRM and MeDIP-PCR analyses revealed that DNA demethylation also up-regulated eIF5A1 after SCT. Consequently, miR-434-3p/eIF5A1 in muscle is a promising potential biotherapy for SCI repair.

Efficacy and site-specificity of adenoviral vector integration mediated by the phage φC31 integrase

Adenoviral vectors deleted of all their viral genes (helper-dependent [HD]) are efficient gene-transfer vehicles. Because transgene expression is rapidly lost in actively dividing cells, we investigated the feasibility of using phage φC31 integrase (φC31-Int) to integrate an HD carrying an attB site and the puromycin resistance gene into human cells (HeLa) and murine myoblasts (C2C12) by co-infection with a second HD-expressing φC31-Int. Because the HD genome is linear, we also investigated whether its circularization, through expression of Cre using a third HD, affects integration. Efficacy and specificity were determined by scoring the number of puromycin-resistant colonies and by sequencing integration sites. Unexpectedly, circularization of HD was unnecessary and it even reduced the integration efficacy. The maximum integration efficacy achieved was 0.5% in HeLa cells and 0.1% in C2C12 myoblasts. Up to 76% of the integration events occurred at pseudo attP sites and previously characterized hotspots were found. A small (two- to three-fold) increase in the number of γ-H2AX positive foci, accompanied by no noticeable change in γ-H2AX expression, indicated the low genotoxicity of φC31-Int. In conclusion, integration of HD mediated by φC31-Int is an attractive alternative to engineer cells, because it permits site-specific integration of large DNA fragments with low genotoxicity.